Why on earth would you want to run less boost, I mean doesn’t more boost equal more power?

Well…yes and no. It is actually possible to make more power with less boost, but changes are required.

By now, everyone should understand the relationship between boost and power. It should come as no surprise that it is almost always possible to make more power by raising the boost applied to a motor. The question is, how then, can the opposite also be true?

The answer requires understanding that there is more to power production than boost, and that pressure alone should never be considered a true indication of power. Though we often label it “positive pressure,” boost is more accurately an indication of back pressure built up in the intake track. Yes folks, that wonderful boost gauge is actually reading how much restriction your engine represents to the airflow provided by (in this case) the supercharger.

This test involved a very simple principle: Let’s rid the system of said restrictions, then watch the power climb. As a side benefit, the boost pressure will also drop.

Expressed as a simple equation to determine horsepower, we combine boost plus the power output of the engine itself. To increase power, you can alter either of the two components in the equation. Increased power can be accomplished by increasing boost pressure from the supercharger OR increasing the power output of the normally aspirated motor you are applying the boost to. You can of course opt to do both, but we kept things simple by altering only the engine side of the equation for this test.

## Comparison Testing

The boost provided by a supercharger is a function of the impeller speed relative to the engine speed. Coupled to this equation is the power output of the normally aspirated motor.

To illustrate what happens to power and boost when we alter the engine side of the equation, we ran a Vortech Ti-trim supercharger on two different test motors. The Vortech was run at the same impeller speed (using the same blower and crank pulleys) with the same intercooler and at the same air/fuel and timing values. The only variable in the equation was the displacement and power output of the two test motors.

## The Test Motors

Test motor number one was a mild 4.8L equipped with a stock block, stock crank and rods, but fortified somewhat with JE forged pistons. To this we added a set of CNC-ported, Trick Flow GenX 205 cylinder heads and mild Stage 1 Truck Cam from Brian Tooley Racing.

Test motor number two was a larger 6.0L equipped with CP/Carrillo forged pistons (and Total Seal piston rings), TEA Stage 2 243 heads and a healthy Comp cam. Both motors were run with the same early truck intake, 75 pound injectors and FAST XFI/XIM engine management system.

## The Dyno Test Results

Before adding boost, we ran each motor in normally aspirated trim to help illustrate both the gains offered by the impressive Vortech supercharger and to see if the difference in power normally aspirated remained constant once we added boost.

First up on the dyno was the mild 4.8L. Sporting the mild BTR Truck cam and TFS heads, the 4.8L produced 398 hp and 353 lb.-ft. of torque. Adding the Vortech supercharger to the mix with the 3.8/7.5 pulley combo and air-to-water intercooler resulted in peak numbers of 746 hp and 592 lb.-ft. of torque. It should be noted that we ran the 4.8L slightly higher than the 6.0L (6,700 rpm), so we will make our comparison at the peak engine speed of 6,500 rpm. Boost supplied by the Vortech started out at 3.1 psi at 3,100 rpm then rose to a peak of 14.6 psi at 6,500 rpm (15.2 psi at 6,700 rpm).

Using the Vortech supercharger, we nearly doubled the power output of the little 4.8L, but now it was time to dyno test the larger 6.0L.

Off came the 4.8L and on went the more powerful 6.0L. Thanks to increased displacement, compression and cam timing, the 6.0L offered considerably more power than the smaller 4.8L in normally aspirated trim. Run on the dyno with the same Fast XFI/XIM management system, the 6.0L produced 549 hp and 481 lb.-ft. of torque. After adding the Vortech blower to the mix, the peak numbers skyrocketed to
896 hp and 724 lb.-ft. of torque.

The power certainly increased, but what happened to the boost?

The boost curve started out at 2.9 psi at 3,100 rpm and rose to a peak of 12.8 psi at 6,500 rpm. Run on the larger 6.0L sporting an extra 150 hp (over the NA 4.8L), the peak boost dropped by 1.8 psi. The change in boost between the two motors increased with engine speed, so the difference would be even greater at 7,000 rpm. The benefit of adding more motor instead of adding more boost is that a reduction in boost will decrease the charge temperature and chance of detonation, while an increase in boost will do the opposite.

Of course, you can always do both and crank up the boost on the bigger motor for maximum effect—just know that it is possible to get more power with less boost.

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